1. Field of the Invention
This invention relates generally to chemical mechanical planarization, and more particularly to methods of and apparatus for optimizing chemical mechanical planarization processes by manipulating a removal profile using one or more diaphragms configured to control localized polishing pressure while capturing free-flowing fluid that is input to the apparatus, wherein the diaphragms also minimize loss of normally-free-flowing fluid from a fluid-bearing.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional integrated circuit devices. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess material.
A chemical mechanical planarization (CMP) system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, a rotary polishing pad, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material or polyurethane in conjunction with other materials such as, for example, a stainless steel belt. In operation, the linear belt polishing pad is put in motion and then a slurry material is applied and spread over the surface of the linear belt polishing pad. Once the linear belt polishing pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the linear belt polishing pad. In this manner, the wafer surface is to be planarized substantially. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A shows a prior linear polishing apparatus 10 which is typically utilized in a CMP system. The linear polishing apparatus 10 removes materials from a surface of a wafer 12, such as a semiconductor wafer. The material being removed may be a substrate material of the wafer 12 or one or more layers formed on the wafer. Such a layer typically includes one or more of any type of material formed or present during a CMP process such as, for example, dielectric materials, silicon nitride, metals (e.g., aluminum and copper), metal alloys, semiconductor materials, etc. Typically, CMP may be utilized to polish the one or more of the layers on the wafer 12 to planarize a surface layer of the wafer.
The linear polishing apparatus 10 utilizes a linear belt polishing pad 14, which moves linearly with respect to the surface of the wafer 12. The surface of the wafer 12 is exposed to the linear belt polishing pad 14. The linear belt polishing pad 14 is a continuous belt mounted on rollers (or spindles) 16 that are typically driven by a motor to provide linear motion 18. A wafer carrier 20 holds the wafer 12 with the surface exposed to a polishing surface 19 of the linear belt polishing pad 14. The wafer 12 is typically held in position by a mechanical retaining ring and/or by vacuum. The wafer carrier 20 positions the wafer 12 relative to the linear belt polishing pad 14 so that the exposed surface of the wafer 12 is forced into contact with the polishing surface 19 of the linear belt polishing pad 14.
FIG. 1B shows a side view of the linear polishing apparatus 10, illustrating the wafer carrier 20 forcing the wafer 12 into contact with the polishing surface 19 of the linear belt polishing pad 14. The linear belt polishing pad 14 may be a continuous belt typically made up of a polymer material such as, for example, the IC 1000 made by Rodel, Inc. layered upon a supporting layer. As the rollers 16 drive the linear belt polishing pad 14 in the linear motion 18 with respect to the wafer 12, a fluid-bearing platen 22 provides a fluid-bearing 24 to support a section of the linear belt polishing pad 14 under an area 26 at which the wafer 12 contacts the polishing surface 19. The support by the fluid-bearing 24 thus opposes a force by which the wafer 12 is forced into contact with the polishing surface 19 of the linear belt polishing pad 14.
The design of the fluid bearing platen 22 has an effect on wafer surface planarity, which is a goal of CMP operations. In an exemplary prior effort to achieve surface planarity in a polishing apparatus of the type of the linear polishing apparatus 10, an attempt was made to control polishing pressure applied by the fluid-bearing 24. In one example shown in more detail in FIGS. 1C and 1D, the attempt was to apply different pressures to different regions 28 (FIG. 1D) of the linear belt polishing pad 14 under the area 26 of contact between the polishing surface 19 (FIG. 1B) and the exposed surface of the wafer 12. The attempt is more fully described in U.S. patent application Ser. No. 10/186,909 filed Jun. 28, 2002 for Fluid Venting Platen For Optimizing Wafer Polishing, which application is assigned to the assignee of the present application, and such application is hereby incorporated by reference. In such application, the different pressures on the regions 28 were to result in different localized polishing pressures applied to the wafer 12, i.e. at wafer locations that correspond to the regions 28. Each different localized polishing pressures was to result from the pressure on the region 28 causing a change in the shape of the supporting layer of the liner belt polishing pad. For example, FIG. 1D shows such change in shape resulting in compression of the polymer material, which in turn was to apply a different polishing pressure to the wafer 12 at the location corresponding to the region 28. In the example shown in FIGS. 1C and 1D, the platen 22 is provided with holes 30 (FIG. 1C) arranged to define zones. In FIG. 1C the zones 32 are designated 32P and 32B as explained below, and are shown configured as concentric circles, for example.
FIG. 1D is an enlargement of a portion of FIG. 1B, and shows sections of the platen 22, the linear belt polishing pad 14, and the wafer 12. Holes 30B are arranged for the zones 32B primarily to provide the fluid-bearing 24, thus the zones 32B are referred to as fluid-bearing zones. Holes 30P are arranged for the zones 32P to contribute to the fluid-bearing 24, but the holes 30P primarily provide the different pressures to the different regions 28, thus the zones 32P are referred to as fluid-pressure zones. In FIG. 1D, one of the holes 30B of the fluid-bearing zones 32B is shown supplying free-flowing fluid (see arrow 34) to provide a pressure P1 of the fluid-bearing 24. This fluid 34 at the pressure P1 flows against the under surface of the supporting layer opposite to the contact area 26. The fluid-bearing 24 is formed by the fluid 34 at the pressure P1 which flows freely in a bearing gap 36 between the platen 22 and the under surface of the supporting layer of the linear belt polishing pad 14. The fluid 34 at the pressure P1 flows freely through the bearing gap 36 and to and through an exit gap 38 that is spaced from a center CL of the platen 22 (see left side exit gap 38 shown radially outward of both the edge of the wafer 12 and the bearing gap 36). The fluid 34 is described as “free-flowing” because the fluid 34 is not significantly restrained from flow through the gaps 36 and 38. The fluid-bearing 24 at the pressure P1 supports the section of the linear belt polishing pad 14 under the area 26 at which the wafer 12 contacts the polishing surface, and reduces the amount of friction between the linear belt polishing pad 14 and the platen 22. To achieve such support of the linear belt polishing pad 14, a fluid supply (not shown) may provide the fluid 34 at a pressure in a range of from 1 to 70 psi. Dynamic losses reduce such supply pressure to provide the fluid-bearing pressure P1 in a range of from 0.5 to 10 psi. Because the fluid 34 is free-flowing, the pressure P1 is referred to as a dynamic pressure. In one example, depending on the diameter of the wafer 12, the fluid 34 may be at the dynamic pressure P1 and be supplied at a volume of about 10 standard cubic feet per second (scfm) for the fluid-bearing zone 32B.
In this example shown in FIG. 1D, the different pressures to be applied to different regions 28 of the linear belt polishing pad 12, and the resulting different polishing pressures, are provided as follows. Those holes 30P that define the particular fluid-pressure zones 32P are also supplied with the fluid 34 from the supply (not shown). These supply pressures are substantially greater than the supply pressures that provide the pressures P1 of the fluid 34 in the zones 32B. The fluid 34 supplied at the greater supply pressure also flows freely from the holes 30P for the zone 32P and against the region 28. This region 28 corresponds to the fluid-pressure zone 32P of the platen 22. Because of the greater supply pressures at which the fluid 34 of the fluid-pressure zone 32P is supplied, dynamic pressures P2 on this region 28 are higher than the fluid-bearing pressure P1. As a result, this region 28 is deformed more than the remainder of the linear belt polishing pad 14 that is deformed in response to the fluid 34 supplied at the fluid-bearing pressures P1. Thus, in response to the fluid 34 at the different pressures P2 at different regions 28 of the supporting layer of the linear belt polishing pad 14, the shape of the supporting layer of the linear belt polishing pad 14 is deformed at locations corresponding to the different regions 28. In turn, the deformed supporting layer compresses the exemplary polymer material on the supporting layer (or permits such material to expand). The compressed or expanded polymer material in turn respectively applies more or less polishing pressure on the exposed surface of the wafer 12 at a wafer region corresponding to the region 28 against which the fluid 34 of the fluid-pressure zone 32P flows.
After flowing against such region 28, the free-flowing fluid 34 of the fluid-pressure zone 32P then freely flows (via the exit gap 38) out of the platen 22 with the freely-flowing fluid-bearing fluid 34 that is at the pressure P1. At the exemplary pressures P2 of the free-flowing fluid 34 of the respective fluid-pressure zones 32P (which are typically adjacent to the edge of an exemplary 300 mm wafer), the volume of the fluid 34 for the fluid-pressure zones 34 may be about 60 scfm, and as described above, is primarily for deformation of the supporting layer of the linear belt polishing pad 14. Thus, the prior linear polishing apparatus 10 requires a fluid supply capable of providing about 70 scfm of the fluid, of which 10 scfm provides the fluid-bearing 24 and 60 scfm is used to obtain the pressures P2 for deforming the supporting layer and the exemplary polymer material of the prior apparatus 10. Since the free-flowing fluid 34 flows through the bearing gap 36 and out the exit gap 38 in this exemplary fluid-bearing 24, and such free-flow is for such fluid-bearing and deformation purposes, the free-flowing fluid 34 must be supplied continuously to establish the exemplary pressures P1 and P2, and at the exemplary 70 scfm volume, which consumes substantial pump energy. Additionally, as the value of the fluid-bearing gap 36 increases, it is necessary to increase the volume of free-flowing fluid 34 that must be supplied through the holes 30, which consumes still more energy for an equivalent deformation of the linear belt polishing pad 14.
As explained above, such prior platens 22 are configured so as to freely-flow the fluid 34 from the holes 30B of the platens 22 to form the fluid-bearing 24 and to freely-flow the fluid 34 from the fluid-bearing 24 to and through the exit gap 38. With such prior platens 22 which rely on use of the fluid 34 at the substantially greater pressures P2, desired final profiles of finished wafers typically cannot be attained when (1) unpolished wafers 12 have a wide range of initial wafer thickness profiles, or there are significant undesired CMP process characteristics, and (2) there is also a requirement to offset such characteristics while minimizing the amount of fluid 34 used to provide the fluid-bearing 24 and to provide such deformation of the linear belt polishing pad 14. Thus, despite the prior arrangement of the platen holes 30P into the fluid-pressure zones 32P to provide selected pressure for such deformation of the linear belt polishing pad 14, there remains an unsolved problem of how to offset such characteristics while minimizing the total amount of fluid 34 used for providing the fluid-bearing 24 and providing such deformation of the linear belt polishing pad 14. This problem is referred to below as the “fluid-conservation problem.”
In view of the foregoing, there is a continuing need for ways to overcome the above-described fluid-conservation problem by controlling localized polishing pressure without using free-flowing fluid, and by minimizing the loss of the free-flowing fluid from a fluid-bearing.